1. Field of the Invention
The present invention relates to an image forming device capable of controlling transfer of paper in a highly accurate manner.
2. Background Art
An image forming device such as a printer was conventionally provided with a stepping motor as a driving source, and a paper transfer mechanism for transmitting rotation of the stepping motor to transfer rollers through gear trains and thereby transferring paper through the transfer rollers.
When a stepping motor is used as a driving source, the amount of transferring paper is controlled by controlling the amount of rotation of the motor using pulse driving.
However, since the transfer amount of paper which is actually transferred cannot be detected by a stepping motor itself, it is only possible to estimate the transfer amount based on the number of driving pulses supplied to the motor and assume that paper has been transferred by the estimated amount.
There are known methods for highly accurately detecting the moving amount of a moving object by irradiating laser light toward the object and detecting speckle patterns appearing in the reflected light. For example, in Publication of Japanese Unexamined Patent Application No. 5-307487, which is incorporated by reference, it is disclosed to detect the moving amount of an object by using speckle patterns generated on the surface of a rotating roller in a mouse. Also, in U.S. Pat. No. 6,220,686, which is incorporated by reference, it is disclosed to perform recording control of a head by using speckle patterns generated on the surface of moving paper. According to these methods for detecting the movement of speckle patterns generated in accordance with the movement of paper, it is possible to detect the moving amount in a highly accurate manner.
However, the contrast of speckle patterns generated in the reflected light from paper may be degraded depending on types or conditions of paper.
For example, it is impossible to obtain speckle patterns with satisfactory contrast when using black paper (paper printed with black color), transparent paper (such as PET film) or paper having a mirror surface.
When the transfer amount of paper is detected by a sensor in the case of a low contrast of speckle patterns, as described above, a detected value is sometimes substantially different from the actual transfer amount, and as a result, controlling the transfer amount of paper using such an inaccurate detected value unnecessarily makes the transfer of paper inaccurate.
The present invention has been made in view of the above points, and it is an object thereof to provide an image forming device capable of reducing transfer errors of paper even when the transfer amount of paper cannot be detected accurately by a sensor.
The above and other objects are achieved by an image forming device which comprises: paper position signal detecting means for irradiating coherent rays of light onto a surface that moves accompanying transfer of paper and for receiving reflected light of the rays of light to generate paper position signals related to positions of the paper; paper transfer amount calculating means for calculating at each specified unit of driving time, through chronological comparison of the paper position signals, a paper transfer amount corresponding to the distance by which the paper has been transferred during each unit of driving time; paper transferring means for transferring the paper by using a driving source at a specified driving speed at each specified time section; paper transfer amount determining means for determining whether or not the calculated paper transfer amount is within a specified normal range at the each unit of driving time; paper transfer amount control value setting means for setting the calculated paper transfer amount as a paper transfer amount control value for a corresponding unit of driving time when it has been determined by the paper transfer amount determining means that the calculated paper transfer amount is within the normal range and for setting a predetermined standard transfer amount as the paper transfer amount control value for a corresponding unit of driving time when it has been determined that the calculated paper transfer amount is outside of the normal range; and time section setting means for setting the time section on the basis of an accumulated value of the paper transfer amount control values.
In the image forming device of the present invention, the paper is transferred at each specified time section, which is defined based on the paper transfer amount control value.
The paper transfer amount control value is set based on determination by paper transfer amount determining means. Specifically, when the calculated paper transfer amount calculated by the paper transfer amount calculating means is within the normal range, the paper transfer amount control value is set to the calculated paper transfer amount, while when the calculated paper transfer amount is outside of the normal range, the paper transfer amount control value is set to a predetermined standard transfer amount.
Therefore, even if the calculated paper transfer amount is substantially different from the actual paper transfer amount for some reason, the paper transfer amount control value, which is set to the predetermined standard transfer amount, will not be substantially different from the actual paper transfer amount.
Accordingly, a substantial error with respect to the time section which is set based on the paper transfer amount control value is prevented, and thus the image forming device of the present invention can perform paper transfer accurately.
The surface that moves accompanying the transfer of the paper here means, for example, the surface of the paper or the surface of a moving member which moves accompanying the transfer of the paper (e.g. the peripheral surface of a roller which rotates accompanying the transfer of the paper).
The time section here corresponds, for example, to the number of pulses by which a stepping motor is driven in the case of using the stepping motor as the driving source, and to the variation of encoder signal in the case of using a direct current motor with an encoder.
According to another aspect of the present invention, there is provided an image forming device which comprises: paper position signal detecting means for irradiating coherent rays of light onto a surface that moves accompanying transfer of paper and for receiving reflected light of the rays of light to generate paper position signals related to positions of the paper; paper transfer amount calculating means for calculating at each specified unit of driving time, through chronological comparison of the paper position signals, a paper transfer amount corresponding to the distance by which the paper has been transferred during each unit of driving time; paper transferring means for transferring the paper by using a driving source at a specified driving speed at each specified time section; correlation value determining means for determining whether or not a correlation value of the paper position signals, which have been compared for calculating the paper transfer amount by the paper transfer amount calculating means, is equal to or higher than a specified reference correlation value; paper transfer amount control value setting means for setting the calculated paper transfer amount as the paper transfer amount control value for a corresponding unit of driving time when it has been determined by the correlation value determining means that the correlation value is equal to or higher than the reference correlation value and for setting a predetermined standard transfer amount as the paper transfer amount control value for a corresponding unit of driving time when it has been determined that the correlation value is lower than the reference correlation value; and time section setting means for setting a time section on the basis of an accumulated value of the paper transfer amount control values.
In the image forming device of the present invention, the paper is transferred at each specified time section, which is defined based on the paper transfer amount control value.
The paper transfer amount control value is set based on determination by paper transfer amount determining means. Specifically, when it is determined by the correlation value determining means that the correlation value of the paper position signals, which have been compared by the paper transfer amount calculating means, is equal to or higher than a specified reference correlation value, the paper transfer amount control value is set to the calculated paper transfer amount, while when it is determined that the correlation value is lower than the reference correlation value, the paper transfer amount control value is set to a predetermined standard transfer amount.
Therefore, even if correlation between the paper position signals compared by the paper transfer amount calculating means is low for some reason (i.e. reliability of the paper transfer amount calculated by the paper transfer amount calculating means is low), the paper transfer amount control value, which is set based on the standard transfer amount, will not be substantially different from the actual paper transfer amount.
Accordingly, a substantial error with respect to the time section which is set based on the paper transfer amount control value is also prevented, and thus the image forming device of the present invention can perform paper transfer accurately.
The correlation here means the degree of agreement between the waveforms of the paper position signals.
According to a further aspect of the present invention, there is provided an image forming device which comprises: paper position signal detecting means for irradiating coherent rays of light onto a surface that moves accompanying transfer of paper and for receiving reflected light of the rays of light to generate paper position signals related to positions of the paper; paper transfer amount calculating means for calculating at each specified unit of driving time, through chronological comparison of the paper position signals, a paper transfer amount corresponding to the distance by which the paper has been transferred during each unit of driving time; paper transferring means for transferring the paper by using a driving source at a specified driving speed at each specified time section; accumulated transfer amount determining means for determining whether or not the accumulated value of the calculated paper transfer amount from the starting point of the time section is smaller than a specified lower limit distance when the accumulated value of driving times of the driving source from the starting point of the time section has reached a specified determining time; and time section setting means for defining, when it has been determined by the accumulated transfer amount determining means that the accumulated value of the calculated paper transfer amount is smaller than the specified lower limit distance a point of time at which the transfer amount of the paper calculated from the starting point of the time section on the basis that the transfer amount per unit driving time is a predetermined standard transfer amount has reached a prescribed section distance as a terminating point of the time section, otherwise defining a point of time at which the accumulated value of the paper transfer amount control values from the starting point of the time section has reached the prescribed section distance as the terminating point of the time section.
In the image forming device of the present invention, when it is determined that the accumulated value of the calculated paper transfer amount is substantially smaller than the actual paper transfer amount (i.e. when it is determined that the accumulated value of the calculated paper transfer amount from the starting point of the time section is smaller than the specified lower limit distance), the time section is defined based on the predetermined transfer amount instead of the accumulated value of the calculated paper transfer amount.
Therefore, in the image forming device of the present invention, it is possible to define the time section without causing a substantial error even if the accumulated value of the calculated paper transfer amount is inaccurate (i.e. smaller than the actual paper transfer amount).
On the other hand, in the image forming device of the present invention, it is possible to define the time section based on the accumulated value of the calculated paper transfer amount when it is determined that the accumulated value of the calculated paper transfer amount is within a range close to the actual paper transfer amount (i.e. it is determined by the accumulated transfer amount determining means that the accumulated value of the calculated paper transfer amount from the starting point of the time section is equal to or larger than the specified lower limit distance).
According to another aspect of the present invention, there is provided an image forming device which comprises: paper position signal detecting means for irradiating coherent rays of light onto a surface that moves accompanying transfer of paper and for receiving reflected light of the rays of light to generate paper position signals related to positions of the paper; paper transfer amount calculating means for calculating at each specified unit of driving time, through chronological comparison of the paper position signals, a paper transfer amount corresponding to the distance by which the paper has been transferred during each unit of driving time; paper transferring means for transferring the paper by using a driving source at a specified driving speed at each specified time section; accumulated time determining means for determining whether or not an accumulated driving time of the driving source from the starting point of the time section is shorter than a specified lower limit time when the accumulated value of the calculated paper transfer amount from the starting point of the time section has reached a specified determining distance; and time section setting means for defining, when it has been determined by the accumulated time determining means that the accumulated driving time of the driving source is shorter than a specified lower limit time, a point of time at which the transfer amount of the paper calculated from the starting point of the time section on the basis that the transfer amount per unit driving time is a predetermined standard transfer amount has reached a prescribed section distance as the terminating point of the time section, otherwise defining a point of time at which the accumulated value of the calculated paper transfer amount from the starting point of the time section has reached the prescribed section distance as the terminating point of the time section.
In the image forming device of the present invention, when it is determined that the accumulated driving time of the driving source, when the accumulated value of the paper transfer amount control value from the starting point of the time section has reached a specified determining distance, is shorter than a normal range (i.e. shorter than a specified lower limit time), the time section is defined without using the accumulated value of the paper transfer amount control value since the accumulated value of the paper transfer amount control value is considered inaccurate (i.e. larger than the actual value).
Therefore, in the image forming device of the present invention, it is possible to define the time section without causing a substantial error even if the accumulated value of the paper transfer amount control value is inaccurate (i.e. larger than the actual paper transfer amount).
On the other hand, in the image forming device of the present invention, it is possible to define the time section based on the accumulated value of the paper transfer amount control value when it is determined that the accumulated value of the paper transfer amount control value is within a range close to the actual paper transfer amount (i.e. it is determined by the accumulated time determining means that the accumulated driving time of the driving source is equal to or larger than a specified lower limit time).